1. Field of the Invention
The present invention relates to a flat panel display device, and more particularly, to an organic light emitting display device.
2. Description of the Related Art
In general, an organic light emitting display device is a light emitting display device having characteristics such as a wide viewing angle, high contrast, and/or a rapid response speed. Therefore, it is drawing attention as a next-generation display device.
A conventional organic light emitting display device includes an anode, an organic emission layer disposed on the anode, and a cathode disposed on the organic emission layer. When a voltage is applied between the anode and the cathode, holes are injected from the anode into the organic emission layer, and electrons are injected from the cathode into the organic emission layer. The holes and the electrons injected into the organic emission layer combine with each other to generate excitons, and the excitons are transitioned from an excited state to a ground state to emit light.
FIG. 1 is a plan view of a unit pixel of a conventional organic light emitting display device, and FIG. 2 is a cross-sectional view taken along line I-I′ of FIG. 1.
Referring to FIGS. 1 and 2, an anode 12 is formed on a substrate 10. A pixel defining layer 15 is formed on the anode 12. An opening 15a for exposing a portion of the anode 12 is formed in the pixel defining layer 15. Then, the substrate and the exposed portion of the anode 12 are cleaned. The cleaning is performed to remove from the anode 12 a foreign substance 17 that may be present. However, the foreign substance 17 may not be substantially removed during the cleaning. As shown in FIG. 2, the foreign substance 17 may merely be pushed to (or moved towards) a boundary of the opening 15a (i.e., an interface between the pixel defining layer 15 and the anode 12) and may become lodged at (or attached to) the interface.
Then, an organic emission layer 20 and a cathode 25 are sequentially disposed on the exposed portion of the anode 12. When the organic emission layer 20 is disposed, portions of the organic emission layer 20 may be broken and/or caused to have a very small thickness in a vicinity of the foreign substance 17. Here, the anode 12 and the cathode 25 may become short-circuited at the broken portion and/or the very thin portion of the organic emission layer 20 (see, for example, area E in FIG. 2), thereby causing a dark pixel to form on the organic light emitting display device.
FIG. 3A shows a photograph of a foreign substance lodged at a boundary of an opening, and FIG. 3B shows a photograph of a cross-section of a substrate that is cut about the foreign substance. Like (or same) reference numerals shown in FIG. 3B designate like (or same) elements shown in FIG. 2.
Referring to FIGS. 3A and 3B, the foreign substance 17 is lodged at (or attached to) the boundary of the opening 15a that is for exposing a portion of the anode 12, and therefore, the emission layer 20 is opened by the foreign substance 17. As a result, the cathode 25 formed on the emission layer 20 may become short-circuited to the anode 12 at the opening of the emission layer 20 (see, for example, area E in FIG. 2). Here, a dark pixel is thereby formed due to the short-circuit at area E.